1. Field of the Invention
The present invention relates to a hard disk drive, and more particularly, to an apparatus for controlling on-track operation in which an actuator is brought on a predetermined position of a track, and to a method thereof.
2. Description of the Related Art
A hard disk drive is an auxiliary computer memory which stores and retrieves information on a disk using a magnetic head. Two types of motors are used to drive the hard disk drive: a spindle motor for rotating a magnetic disk and a voice coil motor for locating the magnetic head on a target track. The voice coil motor is a linear motor, and is driven by a magnetic force by applying current to a coil in a magnetic field formed by a magnet.
Meanwhile, if the power supply of the disk drive is turned off, the spindle motor stops rotating and the head loses its buoyance, so that the head is parked automatically in a parking zone of the disk. At this time, if external vibration or impact is applied to the hard disk drive, the head contacts a data zone of the disk and can cause hard defects, thereby damaging the disk and losing data. The disk having the hard defects cannot be read or written. Thus, a latch is required to hold an arm on which the head is mounted, with a constant force, to avoid the above problems.
Unlatching is opposite to latching, i.e., a routine in which power is applied to the hard disk drive, various integrated circuits (ICs) are initialized in software, and further the actuator moves from the parking zone to a data zone. The unlatch operation is performed by applying an unlatch current to the voice coil motor, and involves initially seeking or on-track, bringing the actuator on a predetermined track. If the unlatch current applied to the voice coil motor in order to move the actuator is excessively high, then the disk, when the actuator is unlatched, in an inner or outer disk can be impacted, which can thereby damage the head and the disk.
Also, even if the actuator is positioned in the data zone, since disturbance of various devices or circuits is not known, it is difficult to bring the actuator on-track in an initial state. That is, after applying the unlatch current, the actuator has a high speed due to disturbances such as air resistance, bearing friction or offset of the circuit during the initial seek or on-track, so that it is very difficult to perform the initial on-track. The disturbances caused by the apparatus are regular, and typically can be corrected by calculating a mean of the offset. However, since various integrated circuit (IC) and passive elements are random, it is almost impossible to estimate the offset of the circuit.
Accordingly, in order to reduce the influence due to the external disturbances during the initial on-track or seek, there have been developed a bearing having low friction, and a suspension for reducing the air resistance. Further, in order to reduce the offset of the circuit, devices having high accuracy are used. However, all these increase the cost. Also, when the disturbance cannot be reduced, it is difficult to develop a device having high Tracks Per Inch.
U.S. Pat. No. 3,994,016 to Moghadam entitled Head Positioning Servo System for Disk Drives, discloses a closed loop head positioning servo system for use in a disk drive employing a disk pack having a dedicated servo surface and a number of data surfaces carrying both data and servo information. It is disclosed that a track counting coarse positioning system is used to move the heads in a ganged assembly to the vicinity of a desired cylinder. A fine positioning system includes one error circuit for generating an error signal representing the deviation of a servo head from a desired cylinder on the dedicated servo surface. Another error circuit generates a second error signal representing the offset of a selected data head from a selected data track in the same cylinder. Analog circuits combine the error signals to produce an output signal which, when applied to an actuator, centers the selected data head on the selected track.
U.S. Pat. No. 4,419,701 to Harrison, et al. entitled Data Transducer Position Control System for Rotating Disk Data Storage Equipment, disclose a system for controlling the position of a head carriage structure of a rotating disk data storage system that includes circuitry for generating a polyphase track boundary signal which compensates for drift, and which doubles or further increases the track density to increase storage capacity. A track centerline sensor circuit is simplified by including the function thereof as microcode routines within a dedicated digital control processor. Error signals are measured periodically across the entire useful field of the disk, and they are constantly updated, so that compensation for drift, runout and offset of the disk relative to the data transducer is achieved. Track overshoot during track seeking movements of the transducer is accommodated, enabling reduced track average access time.
U.S. Pat. No. 4,524,397 to Chalmers, et al. entitled Head Positioning System for a Disc Data Store, disclose a disc data store, wherein a read/write head is radially positionable by a feedback servomechanism to interact with a selectable one out of a plurality of radially equispaced data storage tracks on a rotary disc. Positioning errors resultant from phase errors between the plural signals available as the output of an optical grating head position transducer are eliminated by replacing one of the data storage tracks with a servo track by arranging that the period of the recursive, triangular wave position indicating signals from the transducer is equal to twice the radial spacing between tracks on the disc, by selecting as the exclusive-used position indicating signal that one of the plurality of transducer signals which brings the head to the center of the servo track with least offset, and while employing that selected signal or its generated inverse as the feedback signal to the servomechanism applying that least offset as a correction when positioning the head over data storage tracks.
U.S. Pat. No. 4,797,756 to Yoshihara, et al. entitled Method for Positioning Head in Disk Drive Deriving xe2x80x9cPositionxe2x80x9d Offset from xe2x80x9cQuadraturexe2x80x9d Signals, disclose for a disk drive servo system using position and position-quadrature signals, a method for automatically effecting xe2x80x9cAbsolute Track Registrationxe2x80x9d and compensating for xe2x80x9coffsetsxe2x80x9d by using the peak position of one of the signals to find a xe2x80x9ctruexe2x80x9d position (true offset) for the other, wherein the R/W actuator is brought to rest at a reference position and a sample-offset signal generated, while the corresponding magnitude of related positioning signals are detected. This is repeated until the peak values of the positioning signals are located, whereupon the corresponding position-offset is derived as xe2x80x9ctrue offsetxe2x80x9d, the actuator then being repositioned by the xe2x80x9ctrue offsetxe2x80x9d value; and repeating this for a given number of track sites across the disk.
U.S. Pat. No. 4,812,726 to Benii, et al. entitled Servo Circuit Positioning Actuator, disclose a servo system for controlling the position of an object in accordance with a servo signal, employing an A/D converter to normalize an error in the position of the object and to enable digital correction of an offset in the system and digital compensation for track jumping and drop outs.
U.S. Pat. No. 4,954,907 to Takita entitled Head Positioning Control Method and System, discloses a data recording disk file, wherein head positioning servo information is located in sectors angularly spaced around the disk, and utilizes a head positioning control system for data track following. The control system includes timing circuitry and head position detection circuitry for generating, respectively, a servo sector initiation signal and a signal representative of the head position relative to the centerline of the desired data track to be followed. The control system also includes a velocity detector for determining the velocity of the head relative to the data tracks, a microprocessor for computing an actuator input current signal for moving the actuator and the attached head so as to maintain the head on the desired data track between servo, and memory storage means for storing predetermined constants and values of previously measured head velocity and previously computed actuator input current signals. In response to the servo sector initiation signal, the microprocessor computes a new actuator input current signal based upon the new measured head position, the new measured head velocity, the previously measured head velocity, the previously computed actuator input current signal, and predetermined stored constants, and outputs this new current signal to the actuator. The microprocessor computation takes advantage of the fact that the disturbance to the position of the head during track following and between servo sectors is directly related to the difference between the actuator acceleration of the head and the previously set head acceleration.
U.S. Pat. No. 5,184,257 to Koga, et al. entitled Head Positioning Control for a Spindle Motor Disk Drive, disclose a disk drive including a data recording disk and disk head for recording data and reproducing data from the disk. It is disclosed that arms support the disk head. An actuator drives the arm moving the disk head to a predetermined data recording track of the disk. A spindle motor rotates the disk. An actuator unit moves the disk head to select a track on the disk. First positioning data for positioning the disk head is provided on at least one data surface. Second positioning data is provided on at least one data surface. A control is coupled to the actuator for controlling the positioning of the disk head and the searching of the disk in response to the first and second positioning data. The second positioning data can be located on positioning tracks not used for data. The second positioning information as part of a second positioning data is stored. The disk head position is compensated by the stored second positioning information which is superimposed with the first positioning data.
U.S. Pat. No. 5,189,653 to Yanagi entitled Optical Disk Device Eliminating Offset of Actuator and Offset Eliminating Method Used Thereby, discloses an optical disk device for eliminating an offset of an actuator which controls a fine adjustment of a tracking control. In the device, during an offset measuring mode, an electric drive current of the actuator is changed and the drive current is stored and held when a detection output at a neutral position in a position detector of the actuator is obtained. Then, during a usual operation mode, the obtained offset current is constantly supplied as the drive current of the actuator, whereby a spring force is cancelled and an offset of the tracking error signal is eliminated.
U.S. Pat. No. 5,235,478 to Hoshimi, etal. entitled Disc Drive Apparatus with Servo Tracks Offset from Data Tracks, discloses a disc drive apparatus with a tracking servomechanism, including at least one disc medium having data surfaces where servo signal and data signal are recorded; transducer means having a first head for reproducing the data signal from the data tracks in a playback mode, and a second head for recording the data signal on the data tracks in a recording mode; a rotary arm for supporting the transducer means at one end thereof; actuator motor means for driving the rotary arm in a manner to move the transducer means over the data tracks; servo signal processing means for receiving and processing the servo signal reproduced by the transducer means and outputting first and second servo control signals; and positioning control means for controlling the actuator motor means in the playback and recording modes respectively in accordance with the first and second servo control signals so that the first head of the transducer means is positioned precisely on any selected one of the data tracks in the playback mode and also that the second head is positioned precisely on any selected one of the data tracks in the recording mode.
U.S. Pat. No. 5,251,194 to Yoshimoto, et al. entitled Techniques for Controlling Beam Position and Focus in Optical Disk Drives, disclose an optical disk drive for recording an reproducing information on an optical disk medium including a servo circuit for controlling tracking of a light beam on a predetermined track and a servo circuit for controlling focus of the light beam on the disk surface. The disk surface is divided into a plurality of regions, and calibration values for adjusting the servo circuits are determined in each region. The calibration values are stored in a memory and are used to adjust the servo circuits during tracking on a predetermined track. The calibration values include tracking offset values, focus offset values, servo deviation threshold values and sensor gain values. A number of techniques are disclosed for automatically determining the calibration values.
U.S. Pat. No. 5,479,388 to Gondou, et al. entitled Servo Control System for Head Recording And/or Reproducing Information on And/or from Recording Medium, disclose a servo control system for controlling position of a readout head such as a magnetic or optical head which records, reproduces or erases information on or from a magnetic or magneto-optical disk. This servo control system includes an actuator for moving the head toward a required position on the disk, a position detecting circuit for detecting a position of the head relative to the disk, and a signal processing circuit for processing an output signal from the position detecting circuit to provide a control signal to the actuator. When a value of the signal from the position detecting circuit falls within a preselected range, a controller deactivates a servo control operation of the signal processing circuit and modifies controlled parameters used in the servo control operation in response to a disturbance such as vibration of the system.
To solve the above problems, an objective of the present invention is to provide an apparatus for controlling the on-track operation of an actuator in a hard disk drive in which a voice coil motor (VCM) driving unit is disabled after applying an unlatch current to the voice coil motor (VCM), and the voice coil motor (VCM) driving unit is enabled if the actuator stops on a predetermined track, where disturbance of the apparatus is zero.
Another objective of the present invention is to provide a method for controlling the on-track operation of an actuator in a hard disk drive.
Accordingly, there is provided an apparatus for holding an actuator on-track in a hard disk drive on a predetermined position of a track, including a voice control motor (VCM) driving unit, a position detecting unit, and a controller. The voice coil motor (VCM) driving unit applies a predetermined current to drive a voice coil motor (VCM), the position detecting unit reads data read by a head to detect a position of the actuator, and the controller disables the voice coil motor (VCM) driving unit after unlatching the actuator, and enables the voice coil motor (VCM) driving unit if the position detecting unit detects that the actuator is positioned on a predetermined track to bring the actuator on-track depending on the output of the position detecting unit.
Also, there is provided a method of holding an actuator on-track in a hard disk drive on a predetermined position of a track. The method steps for controlling an actuator include: to unlatch the actuator, to disable a voice coil motor (VCM) driving unit, to determine whether the actuator stops on a predetermined track, and to enable the voice coil motor (VCM) driving unit if the actuator stops on a predetermined track, to bring the actuator on-track.